3GPP (3rd Generation Partnership Project) has been examining an EUTRAN (Evolved UMTS Terrestrial Radio Access Network (UMTS: Universal Mobile Telecommunications System)) network called Dual Connectivity in which packet data is transmitted and received between two eNBs (eNodeBs) and a UE (User Equipment).
FIG. 1 shows an example of a configuration of a wireless communication system that implements Dual Connectivity.
The wireless communication system shown in FIG. 1 includes a UE 10, an MeNodeB (Master eNode B, hereinafter referred to as MeNB) 20, an SeNodeB (Secondary eNode B, hereinafter referred to as SeNB) 30, an MME (Mobility Management Entity) 40, and an S-GW (Serving Gateway) 50.
The MeNB 20 is a second base station that operates cells served by the MeNB 20 (MCG: Master Cell Group).
The SeNB 30 is a first base station that operates to cells served by the SeNB 30 (SCG: Secondary Cell Group). Note that cells served by the SeNB 30 are located within a coverage area of a cell served by the MeNB 20.
The UE 10 is a terminal that receives DL (DownLink) packet data from both the MeNB 20 and the SeNB 30. Note that the UE 10 transmits UL (UpLink) packet data only to the MeNB 20, only to the SeNB 30, or to both the MeNB 20 and SeNB 30.
The MME 40 is a core network device disposed in a CN (Core Network) and performs transmission in the C (Control)-plane and mobile management of the UE 10.
The S-GW 50 is a core network device disposed in the CN and performs transmission of packet data in the U (User)-plane.
Note that the MeNB 20 and SeNB 30 are connected via an X2 Interface. Moreover, the MME 40, the S-GW 50, the MeNB 20, and the SeNB 30 are connected via an S1 Interface.
FIG. 2 shows an example of a connection configuration of the C-plane in Dual Connectivity.
The connection in the C-Plane is shown in FIG. 2. The connection of the UE 10, which is in a connected state of Dual Connectivity, is only S1-MME between the MeNB 20 and the MME 40. Further, the RRC (Radio Resource Control) Connection of the UE 10 is present only in a wireless section between the UE 10 and the MeNB 20. That is, there is no RRC Connection at least in a wireless section between the UE 10 and the SeNB 30. However, the SeNB 30 may create signal information related to an RRC message for the UE 10 and transmit the created signal information to the UE 10 via the MeNB 20.
Further, an example of the connection configuration of the U-plane in Dual Connectivity is the Split bearer option configuration.
FIG. 3 shows an example of a connection configuration of the U-plane in the case of the Split bearer option configuration. FIG. 4 shows an example of a connection configuration of Radio Protocol in the case of the Split bearer option configuration.
As shown in FIGS. 3 and 4, in the case of the Split bearer option configuration, DL packet data of the U-plane is transmitted from the S-GW 50 to only the MeNB 20 and not from the S-GW 50 to the SeNB 30. Note that in the configurations of FIGS. 3 and 4, a bearer from the MeNB 20 to the UE 10 is referred to as an MCG bearer, and a bearer from the SeNB 30 to the UE 10 is referred to as an SCG bearer.
As shown in FIG. 4, the UE 10, MeNB 20, and SeNB 30 are each composed of a PDCP (Packet Data Convergence Protocol) layer(s), an RLC (Radio Link Control) layer(s), and a MAC (Medium Access Control) layer(s). Note that the specification of the RLC layer is described in Non Patent Literature 1 (3GPP TS 36.322 V12.0.0).
In the MeNB 20, the DL packet data of the U-plane received from the S-GW 50 is received by the PDCP layers. In this example, one of the PDCP layers of the MeNB 20 (right layer in FIG. 4) can transmit some packet data (PDCP PDUs (Protocol Data Units)) to the UE 10 via a cell served by the MeNB 20 and can transmit some packet data (PDCP PDUs) to the UE 10 via the SeNB 30. That is, the PDCP layers of the MeNB 20 can split the packet data of the U-plane.